1. Field of the Invention
This invention relates generally to a marine diesel cylinder oil containing a special nonionic detergent to improve its spreadability chracteristics. The invention relates also to a process for lubricating marine diesel engine cylinders.
As is well known, the main purpose of a lubricant is to provide a fluid film between moving metal surfaces to prevent metal-to-metal contact. Any portion of the metal surface not covered by the lubricant is a potential site for severe wear, scuffing and corrosion to take place. Premature wear, scuffing or corrosion will necessitate the replacement of parts sooner than normal, resulting in increased maintenance costs. Furthermore, any wear debris can cause damage in other parts of the engine.
In marine diesel engines, particularly the cross-headed type, which uses a separate oil system to lubricate the upper cylinder chamber (piston, rings and cylinder liners) where combustion occurs, the ability of the lubricant to cover all metal surfaces adequately and quickly is of paramount importance. The ability of a lubricant to cover a metal surface is known as its "spreadability" characteristic, which also measures its effectiveness in use.
The method used to lubricate the upper cylinder area of a cross-headed marine diesel engine consists of injecting the lubricant into the cylinder through a series of orifices (quills) that are located around the upper circumference of the cylinder. As the lubricant is injected it runs down and across the cylinder liner providing a film over the surface that should prevent metal-to-metal contact between the cylinder liner, piston rings and piston skirt as the piston travels in the combustion chamber.
The problem addressed by the present invention is based on the observation that in many instances the lubricant does not cover the entire cylinder liner surface, leaving dry spots that are potential wear sites. Usually, the area directly under the quills is covered with an oil film but the area adjacent to the quills is dry because of the oil's poor spreadability.
One method of improving the spreadability of oil over the cylinder liner would be to redesign the injector/quill system. This approach would not only be impractical but would be economically prohibitive. Another means of improving spreadability would be to use a lower viscosity lubricant. However, since marine engines are designed to use SAE 50 grade cylinder oils for proper film strength, a lower viscosity product would not support the stresses occurring in this area of the engine and film breakage might be greater than desired, leaving additional areas of unprotected metal.
Another factor to consider is the increased use of high sulfur oils requiring the spreadability of lubricants to be such that they can be readily dispersed on diesel cylinder surfaces to neutralize acidic combustion products, thus preventing costly cylinder and piston ring corrosion and damage.
2. Description of the Prior Art
The relevant prior art is directed mainly to compositions useful in 2-cycle gasoline engines and not to spreadability in 2-cycle marine diesels. This art includes Belgian Patent 792,960 which uses a polyalkylene glycol of the formula HO(RO).sub.n H where R is a divalent aliphatic radical and n is 2 to 50. Japanese Patent 5 4160401 suggests adding a polyoxyethylene glycol monoalkylether to a two-stroke engine oil to decrease the amount of soot in the exhaust.
Certain properties of the additives used herein are tabulated in the brochure, "Tergitol Surfactants," published by Union Carbide Corporation in September 1975.